Research article Coagulation/flocculation process with polyaluminum chloride for the remediation of oil sands process-affected water: Performance and mechanism study Chengjin Wang, Alla Alpatova, Kerry N. McPhedran, Mohamed Gamal El-Din * Department of Civil and Environmental Engineering, University of Alberta, Edmonton, Alberta T6G 2W2, Canada article info Article history: Received 26 March 2015 Received in revised form 9 June 2015 Accepted 13 June 2015 Available online 25 June 2015 Keywords: Oil sands process-affected water Coagulation Flocculation Polyaluminum chloride Al 13 abstract This study investigated the application of polyaluminum chloride (PACl) for the treatment of the oil sands process-affected water (OSPW). These coagulants are commonly used in water treatment with the most effective species reported to be Al 13 . PACl with 83.6% Al 13 was synthesized using the slow base titration method and compared with a commercially available PACl in terms of aluminum species distribution, coagulation/flocculation (CF) performance, floc morphology, and contaminant removal. Both coagulants were effective in removing suspended solids, achieving over 96% turbidity removal at all applied coag- ulant doses (0.5e3.0 mM Al). The removal efficiencies of metals varied among different metals depending on their pK a values with metal cations having pK a values (Fe, Al, Ga, and Ti) below OSPW pH of 6.9e8.1 (dose dependent) being removed by more than 90%, while cations with higher pK a values (K, Na, Ca, Mg and Ni) had removals of less than 40%. Naphthenic acids were not removed due to their low molecular weights, negative charges, and hydrophilic characteristics at the OSPW pH. At the highest applied coagulant dose of 3.0 mM Al, the synthetic PACl reduced Vibrio fischeri inhibition effect to 43.3 ± 3.0% from 49.5 ± 0.4% in raw OSPW. In contrast, no reduction of toxicity was found for OSPW treated with the commercial PACl. Based on water quality and floc analyses, the dominant CF mechanism for particle removal during OSPW treatment was considered to be enmeshment in the precipitates (i.e., sweep flocculation). Overall, the CF using synthesized PACl can be a valuable pretreatment process for OSPW to create wastewater that is more easily treated by downstream processes. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction The recovery of bitumen through the oil sands mining opera- tions in northern Alberta, Canada, has rapidly increased in recent years with over 2 million barrels per day of oil being produced in 2013 (Alberta Government, 2014). The hot-water bitumen recovery, and following upgrading processes, use about 3 m 3 of water for each m 3 of crude oil production (Holowenko et al., 2002) which generates large volumes of oil sands process-affected water (OSPW). OSPW is highly saline water with a range of organic and inorganic constituents, including metals, anions, organic com- pounds, and suspended particles (Allen, 2008). Some metals and organic compounds make OSPW toxic with known negative im- pacts on aquatic organisms including algae, fish, invertebrates and mammals (Garcia-Garcia et al., 2011; He et al., 2011; Pourrezaei et al., 2011; Wiseman et al., 2013). Due to this toxicity, OSPW is currently stored in tailing ponds near mining sites awaiting adequate treatment prior to being released into receiving envi- ronments (Speight, 2000). The coagulation/flocculation (CF) process is widely used as a pretreatment to other processes including advanced oxidation, membrane filtration, adsorption, or ion exchange processes (Alpatova et al., 2014; Crittenden et al., 2012; Pourrezaei et al., 2011). Commonly used coagulants are trivalent aluminum salts, Al 3þ (e.g., alum; polyaluminum chloride: PACl), iron salts, Fe 3þ (e.g., ferric sulfate; ferric chloride), and organic polymers (e.g., cationic polydiallyldimethylammonium chloride (polyDADMAC); poly- acrylamide) (American Water Works Association, 1999). Using the CF process for OSPW treatment has recently been investigated using alum alone and/or organic polymers (Alpatova et al., 2014; * Corresponding author. 3-093 Markin/CNRL Natural Resources Engineering Fa- cility, Department of Civil and Environmental Engineering, University of Alberta, Edmonton, Alberta T6G 2W2, Canada. E-mail address: mgamalel-din@ualberta.ca (M. Gamal El-Din). Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman http://dx.doi.org/10.1016/j.jenvman.2015.06.025 0301-4797/© 2015 Elsevier Ltd. All rights reserved. Journal of Environmental Management 160 (2015) 254e262